Center support marine boiler with isolated reheater



April 1, 1 L. E. TRIGGS ETAL 3,435,805

CENTER SUPPORT MARINE BOILER WITH ISOLATED REHEATER Filed Dec. 8, 1967 Sheet 4 of 4 INVENTOR.

LEONARD E. TQIGGS ROBEET B. HEDGES ATTORNEY April 1, 1969 I L. E. TRIGGS ETAL 3,435,805

CENTER SUPPORT MARINE BOILER WITH ISOLATED REHEATER Filed Dec. 8, 1967 Sheet 2 of 4 INYENTOR' LEONARD E. 7'2/665 R0552 T B- HE P655 ATTORNEY CENTER SUPPORT MARINE BOILER WITH ISOLATED RBI- EATER Sheet Filed Dec. 8, 1967 n 1 w m w is NW0 I w x -:T i AW M Z 1 m L a T 4 W m D H 1- S raw w a a .7 6 i m. H M 8 V o M a 4 a M IIiIoW U W I H D qlllllllllll l.\ 4 lla| i 4 ill 2 4 f 7 /|./Y./,/ 7 w 6 F 1 4 3 WJM ATTORNEY April 1, 1969 CENTER SUPPORT MARINE BOILER WITH ISOLATED REHEATER Filed Dec. 8, 1967 Sheet 4 of4 2 INVENTOR. LEONARD E- TRIGGs E0852? 9. HEDGES A TTORNE) United States Patent U.S. Cl. 122-1 5 Claims ABSTRACT OF THE DISCLOSURE A large capacity boiler is adapted for operation in a marine power plant operating on a vapor reheat cycle. The unit is vertically supported at a level intermediate to its upper and lower ends to accommodate vertical expansion in both directions and the arrangement of tubes is such as to provide an integral reheater compartment having independently operated burners and being isolated from the gas flow through the remainder of the unit in order to protect the reheater tubes during astern operation of the power plant.

Background of the invention With the advent of larger and faster maritime vessels, it has become necessary to provide marine boilers capable of producing vapor in greatly increased amounts in order to satisfy the needs of these vessels. This, of course, can be accomplished by employing more efficient vapor cycles for the vessels power plants and/or by simply increasproblem by means of the latter solution would result ing the number of boilers on each vessel. To solve the in considerably greater fabrication costs. If the former solution is ignored, higher fuel costs would result. It has therefore been suggested to provide for the expanded vapor requirements of these larger and faster vessels by increasing the size and capacity of the marine boilers that operate in the power plants thereof and also to operate the power plant on a vapor reheat cycle.

The size of any boiler, be it a marine boiler or a stationary boiler, can be increased by increasing one or a combination of its three basic dimensions: height, width or depth (depth is considered to be the dimension measured along the longitudinal axis of the vapor and liquid drums). It is well known that for a typical two-drum marine boiler the depth is the most costly dimension to increase, followed by the height and then the width. It is also well known, however, that in redesigning boilers for increased capacity, an increase in the width dimension is the least effective. Therefore, from the standpoint of economics and over-all unit efficiency steam generators are normally redesigned by extending their vertical dimension in order to increase vapor capacity. This, however, cannot always be readily accomplished in marine boilers. Due to the fact that such boilers are subjected to dynamic loads and vibrations transmitted through the vessel hulls, and since excessive vibrations can be a source of trouble especially at the junction of the tubes with the drums or headers, there is a practical limitation imposed upon the vertical dimension or distance between drum centers that can be employed in marine boilers. Tests indicate that boiler tubes which would respond to modes at 15 and 40 cycles per second would, upon doubling their length, respond to modes at 4, 11, 22, and 38 cycles per second. For ship-building equipment this increased sensitivity to low frequency vibration results in an increased potential for metal fatigue thereby rendering it necessary to limit the unsupported height of all the tubes employed in the unit.

As for increasing the capacity for vapor production 3,435,805 Patented Apr. 1, 1969 ice of a marine boiler through the use of vapor reheat cycles, attempts have often been made to design a marine power plant that employs such a cycle but none has met with complete success. The difiiculty arises as a result of the fact that when the astern turbine is placed in service, steam flow to the ahead turbine and concomitantly to the steam reheater, which is serially connected to the ahead turbine, must be terminated. Such termination of steam flows through the reheater tubes would naturally deprive these tubes of cooling fluid and, were they to be located in a high temperature section of the steam generator, would result in rapid deterioration or burnout of the tubes. Serveral attempts have been made to obviate this inherent drawback to reheat applications for marine service. For example, it has been proposed to locate the reheater tubes in the steam generator in a relatievly low temperature region such as in the gas pass located down stream of the boiler bank tubes in an attempt to subject the reheater tubes to relatively low gas temperatures. This arrangement has been found to be undesirable due to the requirement of an excessive amount of reheater heating surface which naturally requires an excessively large number of tubes resulting in increased cost and space requirements. It has also been proposed to provide a separate furnace, independent of the steam generator, in which to locate the reheater tubes, thereby permitting a termination of gas flow across these tubes when the exterior turbine is operating and it is desired to terminate flow through the reheater tubes. This arrangement also has been found to be unduly expensive both from the standpoint of fabrication costs and space requirements in that additional piping, fuel burning equipment and containment structure is required.

Summary of the invention By means of the present invention there is thus provided a marine vapor generator arrangement that permits increased vapor generation capacity at a reduced cost. A unit constructed according to the teachings of the invention results in an increase in unit size by expanding the vertical dimension of the unit without the normally expected concomitant danger of subjecting the tubes to undue metal fatigue as a result of vibration and other dynamic loadings characteristic of marine operation. Moreover, the herein disclosed vapor generator design also incorporates a provision for a vapor reheater integral with the unit setting and arranged in such a manner that th tubes that comprise the reheater will not be subjected tt; undue heating during astern operation of the power p ant.

The above objectives are accomplished by providing a marine vapor generator having a furnace section, a boiler section, and a vapor heating section all contained within a single, fluid-cooled containment structure or setting. The furnace section of the unit is vertically elongated and comprised of two groups of tubs connected for series flow by means of a header that surrounds the setting on three sides and that is disposed at substantially the same elevation as the lower drum. Means are provided to support this header and the lower drum by structurally connecting them to ships steel such that pressure parts of the unit will expand both upwardly from this support header and downwardly therefrom. By means of this arrangement the unsupported length of all the tubes is held well within limits that prevent damage due to vibration and other dynamic loading.

To effectively provide for reheat, the convection section of the unit is divided into two laterally adjacent compartments, one of which contains the superheater and the other, the reheater. This latter compartment is provided with burners that operate independently from those that supply heat to the furnace and superheater thereby enabling the operation of the former to be terminated during periods of astern operation of the power plant in order that temperatures within the reheater compartment can be maintained below those that would cause damage to the reheater tubing.

Brief description the drawings FIGURE 1 is a schematic representation of a marine power plant equipped with a vapor generator constructed according to the present invention;

FIGURE 2 is an elevational side section of a vapor generator according to the invention taken along line 2-2 of FIGURE 4;

FIGURE 3 is an elevational side section of the vapor generator taken along line 33 of FIGURE 4;

FIGURE 4 is a front elevational section of the vapor generator of FIGURE 1;

FIGURE 5 is a plan section taken along line 4--4 of FIGURE 3; and

FIGURE 6 is a partial view illustrating the section indicated as 5 in FIGURE 3 in greater detail.

Description of the preferred embodiment Referring now to FIGURE 1 of the drawing, there is shown a schematic representation of a marine power plant installation 10 adapted to operate on a reheat steam cycle in accordance with the teachings of the invention. The installation 10 comprises a steam generator 11 including a superheater 12 and a reheater 14 adapted to supply high temperature steam to an ahead turbine 16 consisting of separate high and low pressure stages, and an astern turbine 18. The ahead and astern turbines 16 and 18 are connected in parallel to a high temperature steam manifold 20 which includes ahead and astern throttles 22 and 24, respectively, and a line 26 and valve 28 for supplying steam to the vessel auxiliaries. The system is intended to operate as follows. When it is desired to propel the vessel in the forward direction, the ahead turbine 16 is placed in service by opening ahead throttle 22 and closing astern throttle 24. High pressure, high temperature steam is then supplied by the steam generator 11, passing from the outlet of the superheater v12 to the inlet of the high pressure stage of turbine 16 where it is expanded to a lower pressure and temperature in driving the turbine and its connected propulsion unit. The steam exhausted from the high pressure stage of the turbine 16 is then returned to the steam generator 11 where it is heated to an elevated temperature in flowing through the reheater 14 prior to being passed to the low pressure stage of the turbine from whence it is discharged to a condenser (not shown).

When it is desired to propel the vessel rearwardly, steam flow to the ahead tunbine is terminated by closing the throttle 22. The astern throttle 24 is opened and high pressure, high temperature steam is passed from the outlet of the superheater 12 to the astern turbine \18 where it is expanded in driving the turbine and the astern propulsion unit before being passed directly to the condenser.

The vapor generator 11 of the present invention is of the two-drum type and has an enclosure or setting that is generally rectangular in horizontal and vertical section. The setting includes a boiler section 30 that extends substantially the full width of the setting and which opens at its rear into a combustion gas outlet plenum 32. The boiler section 30 is connected in open, gaseous communication with a fuel fired furnace chamber 34 through a convection section 36 that houses the vapor superheater 12. As shown best in FIGURES 3 and 4, the convection section 36 and upper portion of the furnace chamber 34 extend laterally only part way across the width of the setting, the remaining portion thereof containing an isolated, separately fired compartment 38 that houses reheater 14, as hereinafter fully explained.

The boiler section 30 comprises a pair of horizontally .4 disposed, laterally extending upper and lower drums 40 and 42, respectively, whose longitudinal axes are located in a common, upright plane. The lower drum 42 is vertically supported by means of drum saddles 44 disposed adjacent each end of the drum and which are in turn supported from ships steel (not shown). Upstanding boiler tubes 46 extend between and are connected in fluid communication at their opposite ends to the respective drums 40 and 42. These tubes 46 are disposed in mutually spaced rows to form a tube bank that extends laterally across the width of the setting, the spaces between the tubes permitting the through-flow of combustion gas to the outlet plenum 32. External downcomer conduits 47 connect the two drums 40 and 42 at their opposite ends and serve to supply the lower drum 42 with liquid from the upper drum 40.

The setting is defined by a front wall 48, side walls 50 and 5-1 and rear wall 52 with furnace chamber 34 extending vertically the full height of the forward portion thereof. As shown in FIGURES 2 and 3, the furnace chamber 34 contains a lower portion 54 and an upper portion 56, the former occupying the full transverse width of the setting while the latter occupies only a portion thereof. The remainder of the transverse area of the upper portion 56 of the setting contains the reheater compartment 38. Division of the furnace chamber '34 into the two portions 54 and 56 can be taken to be at a header complex disposed about the setting at the level of the lower drum 42. This complex is defined by four horizontally disposed headers 58, 60, 62, and 64, the header 58 being a laterally extending header disposed in the front wall 48, while the remaining headers extend from front to rear of the setting having their opposite ends attached to the header 58 and lower drum 42, respectively. The outermost headers 60 and 62 of this latter group are disposed in the side walls 50 of the setting. For reasons hereinafter explained the headers 60 and 62 are merely attached to but do not communicate with the lower drum 42, their function being to serve as relief headers for the tubes lining the lower portion 54 of the furnace chamber and to supply those tubes that line the upper portion thereof. The header 64 at one end, on the other hand, is attached to and communicates with the lower drum 42. At its other end the header is merely attached to but does not communicate with the front wall header 58. A diaphragm 65 (FIGURE 5) is provided in the header 64 to isolate the rearward portion thereof through which liquid from the lower drum is caused to circulate from the forward portion Where no fluid circulation occurs.

Vertical supports 66 are spacedly disposed along the length of the headers 58, 60 and 62 and thus, together with the drum saddles 44, provide vertical support for the unit at the level of the lower drum 42. By means of this arrangement all vertical expansion of the pressure parts of the unit disposed above this level occurs in the upward direction while that of the pressure parts disposed below this level occurs downwardly.

The walls of the setting are lined with tubes which are preferably arranged in panels, each comprising a plurality of parallel tubes welded together in side-by-side relation. This form of construction is well known in the art and provides a means whereby the tubular walls form part of the gas enclosing structure of the unit. In the lower portion 54 of the furnace chamber 34, those tubes that line the front wall 48 between the side walls 50 and 51 of the setting are indicated as 68. They extend between the header 58 and a bottom supply header 70 which extends laterally of the setting. This bottom supply header 70 is connected at its ends to the lower drum 42 by means of external downcomer conduits 71 which supply the header with liquid from the drum. As shown, the tubes 68 that connect to the header 70 are reanwardly offset at their lower ends to form part of the furnace floor. The rear wall 52 of the setting is lined with tubes 72 which emanate from the supply header 70. At their upper ends the tubes 72 connect with the upper drum 40'. Panels containing the tubes 72 extend between the side walls 50 and 51 of the setting and are of welded construction from a level adjacent the header complex to the supply header 70. This portion is indicated as 72a. The portion of the tubes, indicated as 72b, extending above the header complex contains tubes that are mutually spaced, both laterally and rearwardly, to form radiant screens for the superheater 12 and reheater 14.

That portion of the tubes 72 indicated as 72a is rearwardly offset at the upper and lower ends of the portion, the latter offset forming part of the furnace floor and the former cooperating with the tubes in front wall 48' to form a constriction or throat 74 disposed between the lower and upper furnace portions 54 and 56, respectively. Openings are provided in portions 72a to accommodate burners 78 that generate combustion gases which flow through the furnace chamber 34 and convection section 36 to the gas outlet plenum 32 and also serve to provide heat for the superheater 12.

The side walls 50 and 51 in the lower portion 54 of the furnace chamber 34 are lined with tubes that emanate from lower side wall headers 80 which extend from front to rear of the setting and which are supplied with vaporizable liquid from supply header 70 by means of feeder tubes 82. The feeder tubes 82 connect between respective headers at spaced points along their lengths. The rearward section of the lower furnace portion 54, i.e., that portion defined by the tubes indicated as 72b, has its ends closed by tubes, indicated as 84, that are vertically upstanding tubes which connect at their upper ends with abbreviated, horizontal headers 86. The headers 86 are connected, in turn, to the headers 60 and 62, respectively, in the midheight header complex by means of relief tubes 88 connected between the headers at spaced points along their length. The remainder of the side wall 50 in the lower portion 54 of the furnace chamber 34, forwardly of the tubes 84, is lined with vertically upstanding tubes 90 that connect between the headers 80 and 60. That section of the side wall 51 located upwardly of the panel 84, on the other hand, is lined with tubes 92 which, as shown best in FIGURE 3, emanate from the lower side wall header 81 in that wall and extend upwardly to connect with header 94, the latter being a horizontally disposed header that is attached to and communicates with the upper drum 40. This header 94 is located in vertical alignment with the header 64 in the mid-height header complex. The tubes 92, as shown, are diagonally offset beneath the reheater compartment 38 and have a portion, indicated as 96, forming a partial enclosure about the forward section of the header 64, thereby protecting this section of the header through which no fluid is circulated against the effects of the high temperature gases flowing through the furnace chamber 34. Above the enclosing portion 96 the tubes 92 extend vertically upwardly to connect with header 94 thereby serving to form the inner wall of the reheater compartment 38 from a point just forward of the screen tubes 72b to the front wall 48.

In the upper part of the setting, i.e. that part located above the mid-height header complex comprising headers 58 through 64, the front wall 48 is lined with tubes 98 extending in side-by-side relation between the side walls 50 and 51. These tubes 98 connect at their lower ends with the front wall header 58 while their upper ends are rearwardly offset to overlie the top of the setting and connect with upper drum 40 thus forming the roof of the unit. The side walls 50 and 51 in this part of the setting are lined with vertically upstanding tubes 100 connecting between the mid-height side wall headers 60 and 62 at their lower ends and upperside wall headers i102 and 104 at the upper ends. Headers 102 and :104 are horizontally disposed headers which overlie and extend parallel with the headers 62 and 64, respectively. They are attached to and communicate with the upper drum 40 and serve to relieve the side wall tubes passing vapor generated therein to the drum. The ends of the panel of boiler tubes 46 are closed by tubes, indicated as 46a, that have their intermediate spaces sealed by welded metal strips or plates 106 as is common in the art. These tubes 46a are co-planar with the tubes and serve to form rearward extensions of the side walls 50 and 51 of the setting.

According ,to the invention, the vapor generator 11 is provided with a compartment 38 formed integrally with the remainder of the setting and adapted to house the reheater 14 in a manner whereby it will be isolated from the gas flowing through the furnace chamber 34 and convection section 26. The compartment 38 Which is substantially rectangular in section is disposed in the upper right quadrant of the setting as viewed in FIGURE 3 and extends rearwardly from the front wall 48 to the boiler section 30. It is separated from the furnace chamber 34 and convection section 36 by a gas impervious division wall 'which is formed at its forward end by the upper, vertically extending portion of the tubes 92 and rearwardly thereof by vertically upstanding tubes 108 which connect at their ends between the headers 64 and 94. The remaining sides of the compartment are formed by the front wall and roof tubes 98 and side wall tubes 100, with the rear being in open, gaseous communication with the boiler section 30. The bottom of the compartment is provided with a fioor formed by fire brick 110 that is vertically supported by horizontally disposed struts 112 extending between and being attached to the headers 62 and 64 by means of brackets or the like.

Openings 1.14 are provided in that portion of the roof that overlies the compartment 38 to accommodate burners 115. These burners 115 are adapted to fire into the forward section of the compartment where the generated gases flow from front to rear of the unit through the reheater 14 to the boiler section 30' and gas outlet plenum 32. The reheater 14 is protected from the radiant affects of the flame by means of the screen tubes 72b. 'Flow of gas through the compartment is in parallel relation to the flow of gases from the furnace chamber 34, the two both flowing to the boiler section 30 and thence into the outlet plenum 32.

As shown in the illustrated embodiment, the superheater 12 and reheater 14 each comprise a bundle of inverted U-tubes connected at their ends to pairs of headers indicated as 116 and 118, respectively. The tube bundles are arranged in substantially mutually adjacent relationship in that area of the unit that is disposed between the boiler section 30 and screen tubes 72b with the superheater tube bundle 12 being disposed in the convection section 36 and the reheater tube bundle 14 in the rearward section of the compartment 38. The two elements are separated from one another in this area by that portion of the gas impervious division wall formed by the tubes .108.

Vertical support for the superheater 12 and reheater 14 is provided by suspending the two elements from the headers that form the mid-height header complex as by means of brackets or the like (not shown). Thus, the superheater 12 has its headers 116 extending between and supported from headers 60 and 64 while the reheater 14 has its headers slung between headers '62 and 64.

The operation of the herein disclosed marine power plant 10 together with the vapor generator 11 is as follows. When ahead operation of the vessel is desired, the ahead throttle 22 is opened and astern throttle 24 is closed thereby connecting the fluid system of the vapor generator 11 including the superheater 12 and reheater 14 to the ahead turbine 16. Vaporizable liquid is admitted to the vapor generator 11 and burners 78 and 114 are placed in service whereby compustion gas generated by both sets of burners is caused to flow in parallel on either side of the division wall coming in heat exchange relation with both the superheater 12 and reheater '14 in flowing to the boiler section 30 and outlet plenum 32. Thus liquid vaporized in the evaporative section of the vapor generator fluid system is caused to be superheated before being passed to the high pressure stage of the ahead turbine 16 and thence reheated before being passed to the low pressure stage thereof.

For astern operation, the ahead throttle 22 is closed and astern throttle 24 is opened to transfer the flow of vapor from ahead turbine 16 to astern turbine 18. With the ahead turbine being disconnected from the fluid system, fluid flow through the tubes of reheater 14 is terminated and all vapor flow thence passes from the superheater 12 to the turbine 18 and thence to a condenser (not shown). At this time operation of the burners 114 is terminated and, due to the isolation of the reheater 14 as a result of the gas impervious nature of the division Wall that separates the con1- partment 38 from the furnace section 34 and convection section 36, the tubes forming the reheater are prevented from coming in contact with high temperature combustion gases which might otherwise damage the tubes by overheating during this period when there is no fluid flowing through them.

It will be understood that various changes in the details, materials and arrangements of parts which have been herein described and illustrated in order to explain the nature of the invention may be made by those'skilled in the art within the principle and scope of the invention as expressed in the appended claims.

What is claimed is:

1. In a marine power plant comprising ahead turbine means including a superheat stage and a reheat stage, astern turbine means including only a superheat stage and means for selectively supplying superheated and reheated vapor to said ahead turbine means or only superheated vapor to said astern turbine means including a vapor generator, said vapor generator comprising:

(a) generally rectangularly disposed front, rear and side walls defining a setting;

(b) means including upwardly extending tubes for fluid cooling said walls;

(c) a furnace chamber throughout the height of said setting;

(d) means for burning fuel in said furnace chamber to produce combustion gases therein;

(e) a boiler section of less height than said furnace chamber extending laterally of said setting between the side walls thereof and being in gaseous communication with said furnace chamber;

(f) a convection section including a superheater tube bank intermediately disposed between said furnace chamber and said boiler section and in open gaseous communication therewith;

(g) a compartment formed integral with said setting in gaseous communication with said boiler section including a reheater tube bank confined to the upper part of said setting in laterally adjacent relation to said furnace chamber and said convection section;

(h) a tubular gas impervious partition separating said compartment from said furnace chamber extending rearwardly from said front wall and terminating short of said boiler section, said partition comprising the upper portions of tubes lining one of said side walls;

(i) and means for burning fuel in said compartment independent from those in said furnace chamber and including means for terminating the operation thereof when only superheated vapor is supplied to said astern turbine.

2. A vapor generator organization as recited in claim 1 including a group of tubes lining the rear wall of the lower portion of said furnace chamber between the side walls thereof, said tubes having their upper portions disposed in mutually spaced relation and disposed to ex tend vertically through said compartment and said convection section forwardly of said reheater and superheater tube banks to form radiant screens therefor.

3. A vapor generator organization as recited in claim 2 wherein said compartment comprises two oppositely spaced sides, one of said sides being defined by a partition separating said compartment from said furnace chamber and the other side by tubes lining the side wall of said setting in the upper portion thereof, said partition including a first group of tubes extending from the front wall of said setting to said radiant screens and having their lower portions lining one of the side walls of said setting in the lower portion of said furnace chamber and second group of tubes coplanar with said first group extending rearwardly from said radiant screens and having their lengths confined to the upper portion of said setting. 4. A vapor generator organization as recited in claim 3 including:

(a) a boiler section having an upper and a lower drum adjacent the upper and lower boundaries of said section and a bank of upright tubes within said section connecting said drum;

(b) a header complex extending horizontally from said lower drum and including header means disposed in the front and side walls of said setting and a header intermediate said side wall headers attaching between said front wall header and said lower drum, said header connecting and supplying fluid to said second group of tubes;

(c) and said first group of tubes including a portion partially enclosing the forward section of said header to protect the same from combustion gases generated in said furnace section.

5. A vapor generator organization as recited in claim 4 including means for vertically supporting said vapor generator including supports attached by mounting said lower drum and said header complex at spaced points thereabout.

References Cited UNITED STATES PATENTS 8/1943 Badenhausen 122-473 5/1947 Boland 122-478 KENNETH W. SPRAGUE, Primary Examiner. 

